Study on the Microstructure and Properties of Zl114a Friction Stir Welded Joint with Forced Cooling

Abstract:

Article Preview

ZL114A was joined by friction stir welding and liquid nitrogen was used to cool the welded joint during the welding process. The Influence of forced cooling on the microstructure and properties of welded jointed was studied. The results show that, when forced cooling is used, the amount of silicon particles in weld nugget zone is larger and the size is more homogeneous, the size of silicon particle in heat-mechanical affected zone is more fine , the grain size of heat affected zone is half of air cooling welded joint and the amount of Al-Si eutectic is smaller than air cooling welded joint. The micro hardness increases after forced cooling is used, the hardness of weld nugget zone is 20Hv higher than air cooling welded joint. The strength of forced cooling welded joint increases 13.6% than air cooling welded joint.

Abstract: The7A52 aluminum alloy of the 30mm thickness was welded by the friction stir welding. The structure and the mechanical property of the welded joint was researched by the optical microscope and SEM, etc. The results showed: the hardness distribution along the cross section weld zone is W shape, TMAZ/HAZ transition zone of the weld joint is the softening zone , The min micro-hardness occurs on the TMAZ/HAZ transition zone of the advancing side. The tensile strength of the weld is 85.8% of the base mental, and it fractured in the TMAZ/HAZ transition zone, and the fracture morphology is dimple morphology.

Abstract: Friction stir weld fatigue test was performed and the microstructure of the welded joint was analyzed on aluminum 2219-T6. The surface morphology, micro-hardness and grain structure of the welded joint were observed. The fracture surface of the welded joint was observed after the fatigue test. According to the observations, there were more dynamic recrystallizations in the nugget zone and the grain size became smaller in this zone. The grains in the thermo-mechanical affected zone deformed obviously and there were more substructures in the heat affected zone. The hardness values were lower in the thermo-mechanical affected zone and nugget zone. The hardness values distribution shape was W in the upper surface of the joint and probably V in the bottom surface of the joint. The fatigue fractures happened mostly in the nugget zone. There were lots of inner-hole defects in nugget zone on the fracture surface by scan observation. These defects could affect the properties of the welded joint.